U.S. patent application Ser. No. 09/574,499, filed May 19, 2000, entitled “Electrographic Position Location Apparatus and Method,” which is assigned to the same assignee as the present application and is herein incorporated by reference in its entirety, describes an apparatus that comprises an antenna system that uses a resistive voltage divider. Such antenna systems could be used in interactive products such as talking globes.
FIG. 1 is a schematic illustration that shows how a resistive voltage divider might be used in an antenna system in an electrographic position location apparatus. FIG. 1 shows a portion of an antenna system including a resistive voltage divider 850 between two terminal nodes 802, 804. The two terminal nodes 802, 804 can be driven by respective AC voltage sources. The resistive voltage divider 850 includes four resistors R1810, R2812, R3814, and R4816 having the same resistance values. Three conducting finger elements 830, 832, 834 are respectively interspersed between the resistors R1-R4810, 812, 814, 816. Each finger element 830, 832, 834 can radiate AC electric field energy.
Each conductive finger element 830, 832, 834 can correspond to a specific location and can transmit a signal that is different than other finger elements. An AC signal can be applied to the resistive voltage divider 850 to cause each finger element 830, 832, 834 to radiate a constant field along its length. For example, an AC bias may be applied to node 802 while node 804 is grounded. The field generated by each finger element 832, 834, 830 varies according to the point at which it is coupled to the voltage divider 850. In this example, the finger elements 832, 834, 830 are straight and parallel. When the signal is applied to the voltage divider 850, a series of parallel equipotential lines characteristic of the signals transmitted by finger elements 830, 832, 834 are generated. The equipotential lines may have characteristics corresponding to the voltages V1-V3, respectively.
When a stylus (not shown) comprising a receiving antenna is placed over, for example, the finger element 830, a signal with a voltage V1 is transmitted by the finger element 830 and is received by the receiving antenna in the stylus. A microprocessor is operationally coupled to the stylus and the finger element 830. It receives the signal information and determines that the stylus is over the finger element 830. The microprocessor can retrieve an appropriate output corresponding, for example, to a printed feature that is over the finger element 830. This output can then be presented to the user.
A housing may be disposed over the finger elements 830, 832, 834. In an illustrative example, the images of the United States, Mexico and Brazil may be printed on the housing and may be respectively located over the finger elements 830, 832, 834. When the user uses the stylus to select the image of the United States, the receiving antenna in the stylus receives the signal of the voltage V1 transmitted by the finger element 830. After receiving the signal, a microprocessor associated with the antenna system can determine that the stylus is over the finger element 830. It can cause a speaker in the system to sound the phrase “the United States” for the user.
The resistive voltage divider 850 can be fabricated as a resistive strip. A cross-section of exemplary resistive voltage divider 850 is shown in FIG. 2. The resistive voltage divider 850 includes resistors R1-R4810, 812, 814, 816. The resistors R1-R4810, 812, 814, 816 can be made of a conductive carbon-based ink and can have different thicknesses due to inherent inaccuracies in the resistor printing process. The thickness differences can lead to undesired resistance variations in R1-R4810, 812, 814, 816.
Although the resistive voltage divider 850 is suitable for its intended purpose, a number of improvements could be made. First, it would be desirable to provide for an apparatus that is less expensive to produce. Each one of the resistors R1-R4810, 812, 814, 816 in the resistive voltage divider 850 goes through a calibration process to ensure, among other things, that the resistance values of R1-R4810, 812, 814, 816 are within an acceptable range. The calibration data is stored in an EEPROM (electronically erasable programmable read-only memory) chip in the apparatus. This calibration process is time consuming and expensive. In addition, the use of an additional EEPROM chip in an electrographic position location apparatus increases the cost of the apparatus. Accordingly, it would be desirable to omit it if possible. Second, it would be desirable to improve the “resolution” of an electrographic position location apparatus. The resolution of an electrographic position location apparatus is generally the ability of the electrographic position location apparatus to distinguish between different, closely adjacent positions on a surface. The closer the positions that the electrographic position location apparatus are able to distinguish, the higher the resolution. To have high resolution, the differences in the heights of the resistors (and in the local conductance of material used in resistors) R1-R4810, 812, 814, 816 in the resistive voltage divider 850 are generally very small in order to achieve the desired voltage differences in the finger elements 830, 832, 834. It is difficult to print resistors R1-R4 with identical heights and resistance values. Accordingly, it is difficult to achieve high resolution (e.g., {fraction (1/10)}th inch accuracy across a 10 inch surface) in an electrographic position location apparatus. Lastly, because the resistors are desirably uniform in resistance, the conductive material used to form R1-R4810, 812, 814, 816 is expensive. It would be desirable if a less expensive conductive material could be used to reduce the cost of any apparatus formed.
Embodiments of the invention address one or more of the problems described above, as well as other problems, individually and collectively.